COMMUNITY FORUM

basement concrete-cracking and dampness

I posted earier about delta fl and now I am trying to approach this question from a different direction. I am wanting to finish a room in my basement in a 1906 home in Portland, Oregon (lots of rain 9 months and not much the other months). The house is built into a gentle sloped hill with the daylight basement in the back. In the front of the house are two huge 100 year old trees--oak and elm.

The room I am wanting to finish has a large crack in the concrete floor that goes out in several directions. There has been some upheaval over the years so that one side of the crack is about 1/8 of an inch higher than the other. I have not really noticed change in the 20 years I have been here.

At times of the year, the floor will get damp looking patches on it--until my dawg died, I thought it was using the basement as an emergency pit stop when I was at work--but I could never catch it. The patches continued after Manda died. Never standing water, just irregular dark puddle shapes on the floor. When I tape plastic down, there is no condensation.

So the person I am working with has suggested getting a concrete sander to even out the concrete for the floor. Then after I was not sure of that, he suggested cutting a two foot hole in the concrete to see if there is a tree trunk there or if something else needs tending to. Then we would fill it back with concrete.

What do you folks think about either of these ideas? We would then use some kind of epoxy to even out the floor.

There could be many reasons for the floor to move. It could be a root or something else is causing the problem. From my experience it could be caused by the house settling or from erosion due to water or a combination of the two. Often when a basement has a water problem the earth below the concrete will erode. Since you probably only have a 4" slab, it can easily shift.

I have tried to salvage floors only to have them move again. Sometimes they move seasonally or just incrementally over time.

Sanding the concrete is extremely dusty and if you do not have proper filtration and ventilation, the concrete dust lingers forever. It is extremely abrasive to the lungs, so proper respiratory protection is advised. Concrete sanding can also be damaging to the surrounding floor. There is a lot of vibration.

You can re-pour the heaved areas, just be careful and run a dehumidifier to absorb all that water that will be coming out of the concrete as it dries.

Most good epoxy floor products (non Home Depot) are a two part system, both being 100% solids. However most of these epoxy products will only flex up to around 18%. So, if your floor moves a lot, the epoxy will not prevent it nor move with it.

Because you have a water issue, I don't know of any product that would be a sure fire fix.

An easy route would be to re-pour the concrete that has heaved and hope for the best.

If you cannot re-pour, you can cut the heaved areas into manageable sections, dig under them and lay them back down to be even with the rest of the floor. Once complete you can stitch the sections to each other and to the surrounding floor and use an epoxy grout to fill in the gaps.

You can always put an epoxy coating on over it, but give the concrete 30 days to cure. Also, the rest of your floor needs to be etched to open the pores to give the epoxy a good surface to attach. An epoxy coating will only add a little bit of strength to the floor, but not enough to stop it from heaving or sinking again.

Thanks so much for your continued thoughts. we did cut out a large area of the concrete where there had been some upheaval. We found that the solidness of the concrete was not as think as one might have wished. We refilled the hole to be even with the floor.

We found a small inch in diameter root under there. It did not look like it would have caused the problem. Strange thing though--when we broke the root in half, which was easy to do, about a/3 of a cup of liquid ran out of it. We are going to level it with one of those 2 pairt compounds.